1. Field of the Invention
The invention relates to a pressure activated check valve and more particularly to a check valve that allows fluid flow in two directions when hydraulic pressure is turned off, and in only one direction when pressure is turned on.
2. Description of The Related Art
Conventional poppet type check valves include a poppet valve and a poppet spring housed within a valve body. The poppet spring exerts a force on the poppet valve in a first direction to seat the poppet valve and prevent fluid from flowing in the first direction. Fluid flowing into the valve in a second direction opposite the first direction exerts pressure on the poppet valve overcoming the force of the poppet spring and allowing fluid flow through the valve body.
Check valves, such as the one described above, are useful in airplane hydraulic systems for allowing hydraulic fluid to flow from hydraulic actuators into a return line while at the same time preventing hydraulic fluid from flowing in the opposite direction.
A typical application of a check valve used in aircraft hydraulic systems is on the return port of a solenoid operated control valve, such as the control valve for a weapons bay door actuator. The check valve allows fluid from the actuator to flow into the return line, but prevents fluid in the return line from flowing back into the actuator when the control valve is turned off. This is primarily a safety feature preventing for example, an actuator leak from draining fluid from an entire hydraulic system. A solenoid control valve, when turned off, closes off the pressure line but allows return line fluid to flow in either direction. This provides pressure relief on the actuator and associated plumbing due to thermal expansion of the hydraulic fluid.
In various actuation systems for an apparatus, it is necessary to operate the apparatus, such as actuators for weapons bay doors, while the the hydraulic system is off. In a typical actuation system for bay doors, the actuators are arranged so that a slightly larger volume of fluid is required to open the door than is required to close the door. With this arrangement, the directional check valve as described would not allow the actuator to draw fluid, thus the actuator would be prevented from fully extending without drawing a vacuum.
Installing a previously developed manually operated check valve would solve this problem, but would require complicated cable runs and pulleys to link the manual check valve to a manual release handle.
The present invention comprises a check valve that is activated to the checked mode by pressure from the airplane hydraulic system. When the airplane hydraulic system is turned off, the check valve assumes an unchecked position allowing fluid to flow through the valve in either direction.
U.S. Pat. No. 4,738,282 discloses a zero leakage valve that assumes a checked position when a hydraulic system is turned off and assumes an unchecked position when a hydraulic system is turned on. This type of valve fails to overcome the problems in the prior art since it is necessary to have a valve that remains in an unchecked position when the hydraulic system is turned off.
It is an object of the present invention to provide a pressure activated check valve that remains in a checked position when an airplane's hydraulic system is turned on, and remains in an unchecked position when an airplane's hydraulic system is turned off.
A further object of the invention is to provide a check valve which may be deactivated without the need for complicated cable runs and pulleys linking the check valve to a manual release handle.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.